The TV RF signals derived from, for example, a TV antenna, a video cassette recorder, or a cable distribution system are generally coupled to a TV receiver by way of a transmission line. Typically, a twin lead transmission line is employed, its wire ends being fitted with spade lugs, for example, made to fit the clamping screw RF input terminals generally provided on the back panel of the receiver. Normally, the tuner portion of the receiver is enclosed within a shielded unit located in the receiver cabinet at a short distance from the back panel and the RF input signal is coupled from the receiver input terminals to the tuner unit by a pair of conductors.
With this arrangement, an interfering signal that may be present at the receiver input terminals together with a desired signal will be coupled to the tuner unit along with the desired signal. Interfering signals which occur outside the normal tuning frequency range of the receiver may be sufficiently strong to cause undesirable interference with desired signals within the tuning range. For example, interfering signals from non-television sources commonly occur at frequencies above the ultra high frequency (UHF) television broadcast band and such signals are known to interfere with UHF TV signals. In order to attenuate such interfering signals, the tuner unit may incorporate one or more wave-traps, which are used despite the added cost they entail. Such a wave-trap may typically comprise a series resonant circuit tuned to the frequency of an expected interfering signal, so as to shunt it to ground through a low impedance. However, when such a wave-trap is incorporated within the tuner unit, circulating currents at the interfering signal frequency will flow inside the tuner unit and these currents will tend to get into the signal path, thus reducing the effectiveness of the wave-trap. It is recognized that it is preferrable to place the wave-trap outside the tuner unit, i.e. between the input terminals and the tuner unit, so as to keep circulating currents at interfering frequencies outside the tuner unit. However, it has been common practice to incorporate wave-trap components within the tuner unit in order to avoid the added expense of separately housing and mounting such components externally to the tuner unit.
In inplementing a series resonant circuit for a wave-trap, it is desirable to avoid utilizing a wire-wound inductor which is relatively costly and which may require adjustments in production. An inductor having an inductance value suitable for a UHF wave-trap can be implemented on a printed cirucit board by using a conductive spiral path. Such an inductor is known from U.S. Pat. No. 4,494,100 (Stengel et al.) issued 15 January 1985. However, spiral form inductors on printed circuit boards tend to be very lossy and to exhibit a low Q (quality factor). Accordingly, such inductors tend to degrade the performance of a resonant circuit.
Plating the inside and outside surfaces of a cylindrical form closed at one end to produce a high voltage capacitor is known from "Low-Loss Ceramics for Radio-Frequency Use", by G. P. Britton, "Electronic Engineering", July 1941, pp. 301-303 and 318. This article also teaches that a helical conductor may be plated on the outside of a solid coil form to produce a stable inductor. The Britton article however is no directed to the fabrication of helical resonators.